rule of thumb-3.73 for manuals, 4.10 for autos...4.10's will give you more go off the line, but if you're worried about gas mileage on the highway, 3.73's might be the way to go...
pretty sure i'm right about that, but someone else will probably have better advice.

Soccerfreak has it pretty much right on. 4.10a for autos. It will cost you about 15 mph on the top end but how much 170 mph driving do you plan on doing.... And take off will give you a lil pup tent. Get the tuner gears combo from American muscle. The tuner is worth it's weight in gold and free tunes for life is unbeatable.i went with 3.90s but I have a manual and 4.10s put my revs a lil high at 80 mph but an auto will rev lower once the torque converter locks up

I had 4.10s in my 01 v6 a lil while back and its a noticeable difference in the low end. Now that I look back on it, it wasn't worth the mileage loss in the long run. I was getting like 12 mpg with 4.10s and a tune + other mods. But yea 4.10s give a good kick to the autos. Big difference- if you get a tune for it. My speedometer didn't work with the stock tune, but it works if you get a tuner. Kind of annoying for me when I wanted better MPG I would put my stock tune on and my speedometer was around 15 mph off. If yours is a daily driver and you are usually short on gas money... don't do it. But if u don't care about MPG then go for it.
At 70 Mph, rpms were at 3 grand. I would try to stay off the interstate with 4.10s since the rpms were high over 65. Driving on the interstate kicked my butt MPG wise.

3.73 vs 3.31 wont be a very big performance increase, maybe .2 tenths in the quarter. Look at your transmission gearing compared to 94-04 and see if its worse, if so 4.10s might work better for you in the end. Mainly look at the final drive ratio.

Looking to buy gears for my 06 GT but not sure which ones to get. The car is an auto and I was looking at the 3.73 or 4.10's. What would give the best performance?

I got 4:10 gears on my 09 gt auto and I love them best mod I bought ji think 4:10 are the best I got mine from ford racing, one bad thing about them is when you change the gears you have to take it to ford so they can work on the cluster

I've got an 08 v6 auto and I went with 3.73's due to all the highway miles I do and mpg went way down I lost about 100 miles per tank of gas I can't even imagine what 4.10's woulda done I'm happy with what I got second best purchase for me.. Right behind my turbo

Looking to buy gears for my 06 GT but not sure which ones to get. The car is an auto and I was looking at the 3.73 or 4.10's. What would give the best performance?

bro 4:10s all the way. go ford racing parts and buy a full assembely gear to go with it from american muscle.
you really dont use that much more gas, you wouldnt even notice the diffirence to tell you the truth. Bro the car take OFF! lol

there is a big noticable diffrence, deff one of the best mods i ever did.

Are you planning to do this yourself? If so you need a special tool to measure pinion depth. Must guys use the rotunda tool but it is pricey. You also will need some carrier shims to set back lash. Other than that you just need some fluid and l/s additive.the gear should include the crush sleeve and pinion nut.

bro 4:10s all the way. go ford racing parts and buy a full assembely gear to go with it from american muscle.
you really dont use that much more gas, you wouldnt even notice the diffirence to tell you the truth. Bro the car take OFF! lol

there is a big noticable diffrence, deff one of the best mods i ever did.

I was told by my local ford dealer gears for mustangs 3.73 for the 4.6 mod motors. But these new stangs the tranny is set for 4.10 gears. The all around gears are 3.73 for the best if mpg and torque. Lower gears gives better mpg but you Lise out on power and the higher the gear you lose out on mpg on highway speeds.

I like the 3.73 for both worlds I do lots of highways driving and then
Race in town. So I like them for that reason and I am getting 23-25 mpg in my stang.

The reason people tell you 4.10 for auto vs 3.73 for manual is simple.

Its the gearing of the transmission that makes this the factor. Automatics have a different set of gearing compared to a manual, also they have one less gear generally. The transmission gearing works with the rear end gear ratio. The 4.10 helps even out the disadvantage the auto has to help make up for the worse gearing. The issue is the overdrive (4th gear) is about the same as the manual trans so it will mean you will have higher rpms in overdrive and thus worse gas mileage due to it by a bit vs 3.73 gears. Both are good.

99-04 will shave off about 2-2.5 tenths, 94-98 about .4-.5 due to the stock gearing for 99-04 is 3.27 and 94-98 is 2.73.

Higher gears make it easier for your car to accelerate (torque amplification) and harder to keep it going (more effort to turn the wheels as it takes more input to get the X rotations). You can help your gas milage in the city by raising the gear but it hurts it on the interstate~ just FYI. On my 01 V6 I lost about 1.5-2mpg with 3.73 vs the stock 3.27 gears on average with about 50/50 (city/highway) driving.

Ya I have an auto so I heard 4.10 is better but for manuals 3.73 is better. But I don't want to lose too much mpg so I'm not sure which ones to go with

bro all im saying is go 4:10s or youll get 3:73s and wish you had 4:10s. i learned when i first started moding my car, go for the gold right away lol dont settle.
and ur looking at like 2700 rpms at 70

Your only going to lose mileage in higher gears so if your not on the freeway alot it's probably worth it to go 4.10's me personally I have an 08 v6 auto and I couldn't be happier with my 3.73's but then again I've never experienced the 4.10's so i can't really say if the extra pull is worth the mpg for me since I do over 30 miles a day on the highway

gears are something that you cant just let anyone "pop" in... if they are not installed correctly they will wear and make noise (whine) and who knows... and once they start making noise guess what... you cant fix em you have to replace them so you MUST be careful who you choose and what brand you choose (gear wise) as some brands can make more noise than others. I like OEM ford motorsports (but the newer ford motorsports are outsourced to motive... which cause more whine than the OEM ford....)

gears are something that you cant just let anyone "pop" in... if they are not installed correctly they will wear and make noise (whine) and who knows... and once they start making noise guess what... you cant fix em you have to replace them so you MUST be careful who you choose and what brand you choose (gear wise) as some brands can make more noise than others. I like OEM ford motorsports (but the newer ford motorsports are outsourced to motive... which cause more whine than the OEM ford....)

A big hell yeah to what SpectorV just said.
so where do you plan to go bro? i got 2 good spots for u

Ok so what kind of 4.10 gears should I get for my 06 GT? And who should I have install them?

Ive been told only go with ford racing. the whine less.
i got two places for you. the first place is where i had mine installed but he was unable to retune my car. great guy good price. If you get the tune with it, take it there cause he'll do it cheap.

the second place is Realspeed, i dont kwno where your at, but thats in long island. looken up, call, speak to jess, shell hook you up. if you dont want to order, you dont have to, theyll do all the work for you.
they are also VERY fair, like crazy honest. Dan is the owner, hes the one who did my custom tune. dans so honest, he owed me like 40 bucks and he ran out of the shop as i was driving away to give it to me. I didnt even realize....he could have just kept it, but they dont work that way.
i thought that was very cool and good indicator of who they are.